1. Field of the Invention
The invention relates generally to an apparatus for, and a method of, providing timing, synchronization and locating information during the electro-optical scanning of an indicia such as for example a matrix code or a signature.
2. Description of Related Art
Bar code scanners normally read bar code symbols by very rapidly and repeatedly scanning a light beam, for example from a laser source, across the symbol or bar code symbol structure to be deciphered. Reflected light from the light and dark areas of the bar code is received by the scanner, with the time delays between the resultant received pulses of light being used as the basis of a calculation to determine the special relationship between light and dark areas which are present in the bar code. Because of natural variations in the scanning speed (both between scans and within a single scan), and other unquantifiable variables such as movement of the scanner in the user's hand during the scanning process, some means of location and synchronization is required to ensure that the received series of light pulses can reliably be converted into the proper spatial relationship. This locating and timing or synchronization information is normally built into the bar code symbol. This can be done in many ways, but one convenient possibility is to include a series of special locating, timing or synchronization lines within the bar code symbol structure, spaced apart by a known distance. Receipt of signals from these lines enables the scanner to correct for any non-uniformities in the scanning speed.
Because of their need for locating and timing information, bar code scanners have not widely been used to decode indicia such as signatures which intrinsically contain no locating or timing information. The problem of scanning signatures has been addressed by U.S. Pat. No. 5,138,140, which is in common ownership with the present application. That patent teaches that one can reliably scan a signature with a bar code scanner, provided that the label on which the signature is written also carries a multi-row preamble identification code in front of the signature, and a corresponding postamble code after the signature. In practice, labels are pre-printed with preamble and postamble codes, and the signatory is asked to sign in the space between them. The codes and the signature are then scanned. The timing information provided by the preamble and postamble codes enables the reflected light pulses from the signature to be accurately converted into a digitised special reconstruction of the signature, held in computer memory.
Although effective to achieve its stated purpose, the teaching of the prior art does require the use of relatively expensive pre-printed labels. This not only adds to the cost, but limits the flexibility of the system since to be effectively scanned a signature has to be written precisely in the specified area between the preamble and postamble codes. Signatures of different sizes are not easily catered for, neither is it easy to generalise the system to allow the scanner to read many types of images, of different sizes and orientations.